PROJECT SUMMARY Title: Urinary Estrogen Metabolites in a 2-Year Soy Trial among Premenopausal Women Soy foods and their bioactive ingredients isoflavones are thought to interact with endogenous estrogens which play an integral role in the etiology of breast cancer. This small grant in cancer epidemiology proposes additional analyses using existing urine samples that were collected as a part of a 2-year randomized soy trial among 220 premenopausal women. We will explore two hypotheses for the potential protective effects of soy against breast cancer that were not part of the original study because the appropriate analytical techniques to measure urinary metabolites of estrogens and isoflavones were not developed at the time but are available now. One is that soy foods alter estrogen metabolism as assessed by an array of steroidal estrogens in urine to a pattern of less genotoxic metabolites. Second, beneficial effects from soy may only be experienced by subjects who have intestinal bacteria that are able to convert dadzein, one of the major isoflavones in soy beans, to equol. The specific aims of the proposed study are to explore the effect of two daily servings of soy on cytochrome alterations of estrogen metabolism as expressed in the formation of urinary 2-, 161-, and 4- hydroxy estrogen metabolites and to examine whether equol excretor status influences the response to soy as assessed by biomarkers for breast cancer risk measured in the original trial and in the current project. Frozen urine samples collected during the luteal phase and stored at -80:C will be analyzed for nine estrogens and metabolites and for equol using liquid chromatography-mass spectrometry. For each of the 198 subjects (98 intervention subjects and 100 controls) who have a urine sample after at least one year of intervention, we will analyze the baseline and the final sample for estrogen metabolites, whereas equol will be measured in the two urine samples with the highest total isoflavone concentration for each woman in the intervention group only. Because subjects in the control group were not consuming soy foods, their equol producing status cannot be assessed. The statistical analysis will apply mixed models to compare levels and patterns of estrogen metabolites by soy treatment, while taking into account the repeated measures. General linear models will be used to compare the different biomarkers by equol status, i.e., steroid hormones, mammographic density, and urinary estrogen metabolites. In addition, we will examine equol producer status in relation to ethnicity, body weight, lifetime soy intake, and other dietary factors. PUBLIC HEALTH RELEVANCE: PROJECT NARRATIVE Title: Urinary Estrogen Metabolites in a 2-year Soy Trial Among Premenopausal Women Public Health Significance: The hormonal effects of soy foods continue to be emphasized in scientific and popular publications and need to be understood better, in particular in light of emerging concerns about potential adverse effects of soy among breast cancer survivors and women at high risk for breast cancer. This project will explore two hypotheses of how soy and isoflavones may protect against breast cancer and will help to understand the role of soy foods in breast cancer development and prevention.